2

I have this temperature sensor (DS18B20). I've followed the tutorial on Adafruit (here). First I had to setup some modules by doing:

sudo modprobe w1-gpio
sudo modprobe w1-therm

Then I check the serial number of the sensor (28-000005b89af). When I used the command cat w1_slave in the correct directory, it printed correctly the temperature (checked it which other thermometer):

a2 01 4b 46 7f ff 0e 10 d8 : crc=d8 YES
a2 01 4b 46 7f ff 0e 10 d8 t=26125 (<--- this is the temperature factor 1000)

But then Adafruit provides me with an python script that isn't running as it should.

import os
import glob
import time

os.system('modprobe w1-gpio')
os.system('modprobe w1-therm')

base_dir = '/sys/bus/w1/devices/'
device_folder = glob.glob(base_dir + '28-000005b89af')[0] #serial number of my sensor
device_file = device_folder + '/w1_slave'

def read_temp_raw():
    f = open(device_file, 'r')
    lines = f.readlines()
    f.close()
    return lines

def read_temp():
    lines = read_temp_raw()
    while lines[0].strip()[-3:] != 'YES':
        time.sleep(0.2)
        lines = read_temp_raw()
    equals_pos = lines[1].find('t=')
    if equals_pos != -1:
        temp_string = lines[1][equals_pos+2:]
        temp_c = float(temp_string) / 1000.0
        temp_f = temp_c * 9.0 / 5.0 + 32.0
        return temp_c, temp_f

while True:
    print(read_temp())  
    time.sleep(1)

When I run it as root I get an error (line 9) device_folder = glob.glob(base_dir + '28-000005b89af')[0] IndexError: list index out of range.

What causes this error? And how can I fix it?

1

That seems overly complicated for the simple task it is performing.

#!/usr/bin/env python

import time

DS18B20="/sys/bus/w1/devices/28-000005d34cd2/w1_slave"

r = 0

while True:

   r += 1

   f = open(DS18B20, "r")
   data = f.read()
   f.close()

   (discard, sep, reading) = data.partition(' t=')

   t = float(reading) / 1000.0

   print("{} {:.1f}".format(r, t))

   time.sleep(3.0)

You could just replace DS18B20 with your devices identifier.

0

I fixed this issue. I believe when you call

os.system('modprobe w1-gpio')
os.system('modprobe w1-therm')

in the python code, the glob tries to access the directory prior to it being created.

I added a time.sleep(5) and I have not had an issue since. Also I'm not over clocking.

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